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The Single UNIX &reg; Specification, Version 2<br>
Copyright &copy; 1997 The Open Group

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<h4><a name = "tag_000_008_297">&nbsp;</a>NAME</h4><blockquote>
sem_init - initialise an unnamed semaphore
(<b>REALTIME</b>)
</blockquote><h4><a name = "tag_000_008_298">&nbsp;</a>SYNOPSIS</h4><blockquote>
<pre><code>

#include &lt;<a href="semaphore.h.html">semaphore.h</a>&gt;

int sem_init(sem_t *<i>sem</i>, int <i>pshared</i>, unsigned int <i>value</i>);
</code>
</pre>
</blockquote><h4><a name = "tag_000_008_299">&nbsp;</a>DESCRIPTION</h4><blockquote>
The
<i>sem_init()</i>
function is used to initialise the unnamed semaphore referred to by
<i>sem</i>.
The value of the initialised semaphore is
<i>value</i>.
Following a successful call to
<i>sem_init()</i>,
the semaphore may be used in subsequent calls to
<i><a href="sem_wait.html">sem_wait()</a></i>,
<i><a href="sem_trywait.html">sem_trywait()</a></i>,
<i><a href="sem_post.html">sem_post()</a></i>,
and
<i><a href="sem_destroy.html">sem_destroy()</a></i>.
This semaphore remains usable until the semaphore is destroyed.
<p>
If the
<i>pshared</i>
argument has a non-zero value,
then the semaphore is shared between processes;
in this case,
any process that can access the semaphore
<i>sem</i>
can use
<i>sem</i>
for performing
<i><a href="sem_wait.html">sem_wait()</a></i>,
<i><a href="sem_trywait.html">sem_trywait()</a></i>,
<i><a href="sem_post.html">sem_post()</a></i>,
and
<i><a href="sem_destroy.html">sem_destroy()</a></i>
operations.
<p>
Only
<i>sem</i>
itself may be used for performing synchronisation.
The result of referring to copies of
<i>sem</i>
in calls to
<i><a href="sem_wait.html">sem_wait()</a></i>,
<i><a href="sem_trywait.html">sem_trywait()</a></i>,
<i><a href="sem_post.html">sem_post()</a></i>,
and
<i><a href="sem_destroy.html">sem_destroy()</a></i>,
is undefined.
<p>
If the
<i>pshared</i>
argument is zero, then the semaphore is shared between threads of the
process; any thread in this process can use
<i>sem</i>
for performing
<i><a href="sem_wait.html">sem_wait()</a></i>,
<i><a href="sem_trywait.html">sem_trywait()</a></i>,
<i><a href="sem_post.html">sem_post()</a></i>,
and
<i><a href="sem_destroy.html">sem_destroy()</a></i>
operations.
The use of the semaphore by threads other than those
created in the same process is undefined.
<p>
Attempting to initialise an already initialised semaphore results in
undefined behaviour.
</blockquote><h4><a name = "tag_000_008_300">&nbsp;</a>RETURN VALUE</h4><blockquote>
Upon successful completion, the function initialises the semaphore in
<i>sem</i>.
Otherwise,
it returns -1 and sets
<i>errno</i>
to indicate the error.
</blockquote><h4><a name = "tag_000_008_301">&nbsp;</a>ERRORS</h4><blockquote>
The 
<i>sem_init()</i>
function will fail if:
<dl compact>

<dt>[EINVAL]<dd>
The
<i>value</i>
argument exceeds
<i>SEM_VALUE_MAX</i>.

<dt>[ENOSPC]<dd>
A resource required to initialise the semaphore has been exhausted,
or the limit on semaphores (SEM_NSEMS_MAX) has been reached.

<dt>[ENOSYS]<dd>
The function
<i>sem_init()</i>
is not supported by this implementation.

<dt>[EPERM]<dd>
The process lacks the appropriate privileges
to initialise the semaphore.

</dl>
</blockquote><h4><a name = "tag_000_008_302">&nbsp;</a>EXAMPLES</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_303">&nbsp;</a>APPLICATION USAGE</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_304">&nbsp;</a>FUTURE DIRECTIONS</h4><blockquote>
None.
</blockquote><h4><a name = "tag_000_008_305">&nbsp;</a>SEE ALSO</h4><blockquote>
<i><a href="sem_destroy.html">sem_destroy()</a></i>,
<i><a href="sem_post.html">sem_post()</a></i>,
<i><a href="sem_trywait.html">sem_trywait()</a></i>,
<i><a href="sem_wait.html">sem_wait()</a></i>,
<i><a href="semaphore.h.html">&lt;semaphore.h&gt;</a></i>.
</blockquote><h4>DERIVATION</h4><blockquote>
Derived from the POSIX Realtime Extension (1003.1b-1993/1003.1i-1995)
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Copyright &copy; 1997 The Open Group
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